Nuclear Fusion Just Got One Step Closer To Reality

October 14, 2013

Image Caption: The international inertial confinement fusion community, including LLNL researchers, uses the OMEGA laser at the University of Rochester's Laboratory for Laser Energetics to conduct experiments and test target designs and diagnostics. Credit: Lawrence Livermore National Laboratory

Much has been made of the energy crisis in recent years. Currently our dependence is predominantly on limited natural resources – coal, natural gas, oil, etc. Alternatives exist, of course, such as solar, wind, hydroelectric, and even nuclear. But each of these has significant drawbacks, whether that is cost, efficiency, or waste.

The solution that everyone is looking to is nuclear fusion, where light atoms are compressed at high energy, forcing them to join into a single nucleus. The process produces more energy than it takes to bring the nuclei together. (This is generally the case for lighter nuclei up to iron, where the process becomes endothermic.)

Fusion reactions rely on the inverse process used by current nuclear facilities, which break heavy ions apart through a process called fission. The result is the release of stored nuclear energy, but it also produces significant radioactive byproducts that need to be disposed of. Yet, despite fusion being the most obvious solution to our energy needs, it has not come to reality.

First of all, the technology is extremely expensive to develop. The National Ignition Facility (NIF) cost more than $3.5 billion to build, not to mention operating costs. Other fusion facilities, such as the European Tokomak reactors, have similar price tags, and none of them have yet proven viable.

The problem is that for fusion to make sense the amount of energy produced by the nuclear reactions must exceed the amount of energy needed to run the reactor, a threshold known as break-even energy, but such energy levels have never evenbeen approached. This is not entirely surprising, as in many cases smaller reactors are built to test technology, knowing that larger reactors would need to be constructed – a process known as scaling-up – to exceed the break-even threshold. However, the energy levels reached have lagged behind that predicted by theory, casting doubt on the viability of fusion reactors altogether.

But new data out of the NIF may provide some hope. The BBC has reported that experiments conducted in September produced more energy than the energy that initiated the fusion reaction, a first for any fusion reactor of any type. This is a significant step because the energy output measured up pretty closely with theoretical predictions. But, there is still much work to do.

The NIF works by focusing 192 laser beams onto a single fuel pellet about the size of a BB. The tiny spheroid is composed of solid forms of the hydrogen isotopes deuterium and tritium, containing one or two extra neutrons respectively. The energy from the lasers compresses these isotopes together, creating hydrogen and helium nuclei, along with other radiation, the energy from which can be extracted.

However, due to known inefficiencies in the facility, the amount of energy required to create the beams is about 10 times greater than the energy that reaches the fuel. So, either improvements in the energy generation of the facility would be needed or tuning of the process is required tor each the break-even threshold, an event NIF researchers call ‘ignition.’

While the ability to use fusion as a replacement for other forms of energy creation is still a long way off, this milestone by the NIF is significant and will hopefully provide a basis for future improvements.